Alkali metal sulfonates include natural petroleum sulfonates, e.g., sodium petroleum sulfonates and synthetic petroleum sulfonates made by the sulfonation of alkyl aromatic compounds. Alkali metal sulfonates are widely used as the primary emulsifier in formulating emulsifiable lubricating compositions used for cutting fluid, hydraulic fluids, metal-working lubricants, and so forth.
Sodium petroleum sulfonates are typically produced as a by-product of refining processes in which certain highly refined petroleum products such as white lubricating oils, medicinal oils, and certain grades of transformer oils, are produced. The highly refined petroleum products are produced by treating a refined petroleum distillate or raffinate with fuming sulfuric acid which reacts with certain components of the oil to produce sulfonic acids, some of which are oil-soluble and some of which are water-soluble, thus forming a two-phase system. The two phases separate into two layers one of which is the oil layer containing the oil-soluble reddish-brown or mahogany sulfonic acids, and one of which is the water-soluble layer commonly referred to as an acid sludge layer that contains resinous materials, unreacted sulfuric acid, and water-soluble or green sulfonic acids. The layers are then separated and the oil-soluble sulfonic acids recovered from the oil layer, usually in the form of their sodium salts.
The mahogany sulfonic acids being preferentially oil-soluble have found wide use in the preparation of emulsifiable petroleum products, such as in soluble cutting oils, hydraulic fluids, metalworking lubricating fluids for forming of metals, and so forth. The acid oil layer is neutralized to make a sodium salt and extracted with a polar solvent, typically alcohol, to separate most of the oil phase, and to increase the activity of the sodium sulfonate. This type of process is discussed generally in U.S. Pat. No. 1,930,488. The manufacture of white oils by the above process has become increasingly uneconomical and as a result, the production of sulfonates as by-products of white oil refining is substantially declining. This has left a significant shortage of sodium petroleum sulfonates.
To cope with this shortage of sodium petroleum sulfonates, applicants have investigated a variety of emulsifier candidates as replacements for some significant portion of the sulfonate emulsifier employed in the manufacture of emulsifiable concentrates of lubricating oils. As a result of these investigations, it has been found that alkali metal alkyl salicylates can substitute for equal weight amounts of alkali metal sulfonates in otherwise known and conventional sodium sulfonate emulsifier compositions intended for use in the production of water-miscible lubricating oil concentrates while achieving similar emulsion-forming properties as the all-sulfonate emulsifier compositions.